The present invention relates to a multilayer interconnection board, especially a multilayer interconnection board suitable for a strip line structure or micro-strip line structure.
It is possible to adjust the characteristic impedance of the multilayer interconnection board by adjusting a thickness of a dielectric substrate made of a dielectric, a dielectric constant of the dielectric, a line width of a signal line, a distance between a ground layer and the signal line, and so forth. However, when the signal line is connected with a capacitive load, such as a through-hole, the characteristic impedance is reduced because of the increase of a capacitive component in the vicinity of the through-hole. If the characteristic impedance is reduced in the vicinity of the through-hole, a signal reflection, which is generated by an unconformity of the impedance, degrades a high-speed signal. Especially, if the through-hole includes a stub, the characteristic impedance is reduced remarkably and the degradation of a high-speed signal becomes serious.
It is disclosed in Japanese Patent Application Unexamined Number 2004-14800 that when a multilayer interconnection board is provided with a pair of signal conductors performing a data differential transmission, the differential impedance can be adjusted by extending the distance between the pair of signal conductors in the though-hole.
The above method, however, cannot be used for a wiring pattern of high density